In the cab of a hydraulic shovel (as an example of the working machine), various types of instruments (indicators) are arranged to let the operator check basic information on vehicle body status of the hydraulic shovel. Such instruments include a coolant temperature indicator, a hydraulic fluid temperature indicator, a fuel level indicator and an engine revolution speed indicator, for example. In addition to these indicators, an hour meter indicating the operating time of the hydraulic shovel, switching position information on the gate lock lever, etc. are also displayed as needed.
In recent years, hydraulic shovels are adapted to display various types of information on the hydraulic shovel (including the information on the above instruments) all together on a monitor such as a liquid crystal display. In normal times, such a monitor displays basic information on the vehicle body status such as the coolant temperature and the fuel level. However, in cases where an abnormality has occurred to the hydraulic shovel, for example, it is necessary to notify the operator of warning information (indicating the occurrence of the abnormality, the contents of the abnormality, countermeasures to be taken, etc.) by displaying the warning information.
Further, since the rearward visual field for the operator manipulating the machine in the cab is insufficient, a monitoring camera is attached to the rear part of the hydraulic shovel and a camera image acquired from the camera is displayed on the monitor. This secures an auxiliary visual field in back of the hydraulic shovel and enables safe operations.
Incidentally, such a monitor is desired to be as compact as possible in order to secure the operator's visual field. Further, the amount of information displayed on the monitor is on the rise in these years with the increase in the functions of hydraulic shovels. It is therefore necessary to efficiently display a larger amount of information in a limited display area.
It is also possible to manually or automatically switch the displayed image among the basic information, the warning information and the camera image. However, the manual switching of the displayed image is undesirable since it forces the operator to perform the switching during the operation and can disturb the operator's concentration. The automatic switching of the displayed image is also undesirable since automatic switching against the operator's intention can occur. In such cases, the operator cannot view a necessary image and that can obstruct the operation.
As a conventional technique for addressing this problem, Patent Literature 1 has proposed a display system which superimposes the basic information and the camera image together in a style allowing the camera image to be viewed through. This superimposition of the basic information and the camera image allows the operator to check the safety with a sufficient rearward visual field while also checking the vehicle body status of the hydraulic shovel. However, even this technique has a problem in that the image quality of the superimposition area in the camera image deteriorates in some degree and the area becomes hard to see. To deal with this problem, the superimposition area is set in a part of the camera image corresponding to the left rear view from the hydraulic shovel. For the left rear range, the operator checks the safety by performing both the direct visual check (by turning around) and the visual check via a rearview mirror.
There has also been proposed a display system which superimposes the warning information (instead of the basic information) and the camera image together in a style allowing the camera image to be viewed through.